The present invention relates to a liquid crystal display device and, more particularly, to a guest host type liquid crystal display device with a high display contrast.
Guest host type liquid crystal display devices are characterized by that they include a thin layer of a host liquid crystal material in which a pleochroic guest material is dissolved. It is known that the alignment of the host liquid crystal material by the application of an electric field, such as nematic liquid crystal, can be used to orient guest molecules dissolved in the host. Such is disclosed in Taylor et al., U.S. Pat. No. 3,833,287, Sept. 3, 1974 "GUEST-HOST LIQUID CRYSTAL DEVICE".
Conventionally, the host liquid crystal layer is held by a pair of substrates positioned in parallel and with a certain separation distance. The display device is called a positive type in the cast where the electrode means shapes the direct or positive form of a display symbol to be indicated.
When an electric field is applied to the electrode means, the longitudinal axis of the guest molecule adjacent the electrode means is directed in the direction of the electric field. Color by this guest molecule becomes deep. Simultaneously, there is a tendency for color provided by the absorption spectrum in the direction of the minor axis of the guest molecule far from the electrode means to become deep to a certain degree. Therefore, only poor display contrast is provided.
In the case where the display device is a negative type in which the electrode means shapes the negative form of the display symbol, a similar problem is present.
Therefore, it is desired that the display contrast of such a display device be improved to provide a good practical device.